[viostor] Fix SRB Extension struct member alignment

[benyamin-codez]

Refactors to fix a struct member misalignment in _SRB_EXTENSION:

1. Creates a new _SRB_EXTENSION_FLAGS struct of 32 bits length
2. The first bit is fua (Forced Unit Access)
3. The other bits are unused padding
4. Replaces the _SRB_EXTENSION member fua with new flags member
5. Updates references to srbExt->fua to use srbExt->flags.fua
6. Enforces 1-byte alignment of structs _SRB_EXTENSION and _SRB_EXTENSION_FLAGS

[gemini-code-assist]

Summary of Changes

Hello @benyamin-codez, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses and resolves a struct member misalignment issue within the _SRB_EXTENSION structure in the viostor driver. By refactoring the fua flag into a dedicated, properly padded _SRB_EXTENSION_FLAGS struct and adjusting the member order within _SRB_EXTENSION, the changes ensure correct memory alignment. This is critical for stability and preventing potential data corruption or undefined behavior in low-level driver operations, ultimately improving the robustness of the driver.

Highlights

• New Struct for Flags: A new _SRB_EXTENSION_FLAGS struct has been introduced to encapsulate the fua flag and ensure proper alignment.
• FUA Flag Encapsulation: The fua (Forced Unit Access) flag is now the first bit within the newly created _SRB_EXTENSION_FLAGS struct.
• Struct Padding: Padding bytes have been added to the _SRB_EXTENSION_FLAGS struct to guarantee a 32-bit length and correct memory alignment.
• SRB_EXTENSION Modification: The direct fua member in _SRB_EXTENSION has been replaced with an instance of the new SRB_EXTENSION_FLAGS struct, named flags.
• Code References Updated: All existing references to srbExt->fua have been updated to srbExt->flags.fua to reflect the new struct hierarchy.

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[YanVugenfirer]

[Jenkins CI]: Can one of the admins verify this patch?

[benyamin-codez]

Will rebase following merge of #1467 or #1468...

[gemini-code-assist]

Code Review

This pull request correctly addresses a structure member misalignment issue in _SRB_EXTENSION by reordering its members. The change to introduce an _SRB_EXTENSION_FLAGS struct for the fua flag is a good approach. However, the implementation of _SRB_EXTENSION_FLAGS seems to deviate from the stated intent in the pull request description, resulting in a larger-than-necessary struct and an inefficient memory layout. I've provided a suggestion to align the implementation with the description, which will result in a more efficient memory layout.

[kostyanf14]

ok to test

[benyamin-codez]

@kostyanf14

I'm not sure this one will work. I ended up with BSODs in my stress tests for both 32 and 16 bit members. I'll try to test some more in coming hours, but in any case, I think this one is likely to get another push... Methinks it might be better to just wrap the extension in a pragma pack (1) and keep the fua bit in the extension. Anyway, I'm minded to run up some variants in the debugger and try to see what is actually happening...

[kostyanf14]

@benyamin-codez so you also can reproduce bsod with qcow2 image and viostor. Am I correct?

[benyamin-codez]

@benyamin-codez so you also can reproduce bsod with qcow2 image and viostor. Am I correct?

@kostyanf14, with the changes in this PR in my WIP, yes, I get BSODs on qcow2 images.

I haven't checked it as is because without the other changes, it will likely get BSODs anyway.

I don't get the BSODs with PR #1467, even on qcow2 images.

It is the combination of pragma pack(1) wrapping and the fua change. With just the (incorrect 32 byte) fua change it was ok. I just need to flesh it out a bit more, hopefully in the next few hours, but it will still need to be after rebasing on #1467 / #1468, if that merges.

[benyamin-codez]

@kostyanf14

By way of update:

I've gone with a different and more simple approach here that is just as effective.
I'll force-push a new commit when my time permits...

I note this only helps to resolve the BSODs and 4KiB block write performance, and not the QCOW2 issue.

cc: @YanVugenfirer @vrozenfe

[YanVugenfirer]

@benyamin-codez - Please rebase.

[benyamin-codez]

Please rebase.

@YanVugenfirer

As mentioned above, I went a different (wholistic - imho better) path with this. I just need to do some recalculations and tests following the blk_discard_write_zeroes moves @kevmw made with the relevant structs. I don't think anything changed because, iirc, they still aligned with 4 and 8-byte boundaries, but I just want to check to be sure.

I think a new PR is probably best.
I'll close this one as soon as I raise the new one.